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If you remember, a couple months ago my neighborly engineer whipped up the first part of a three part series discussing heating and cooling recommendations for older homes. The idea was to provide quality info for folks at all levels of the socioeconomic spectrum. From the rich financially gifted to the poor financially challenged. And now after two long months, part two is here. I’m sure you all have been waiting with unfettered anticipation…I know I have.
So here ya go.
My middle-of-the-road recommendation consists of two parts:
#1: Mini duct system – “An air distribution system based on a principle known as aspiration, where the air is injected into the room at a much higher velocity (i.e. 1600 – 2000 ft./min.) than with conventional air conditioning systems (i.e. 300 – 400 ft./min.). As a result, the system provides complete air circulation throughout the space, eliminating the typical 2-3 degree temperature stratification between the floor and ceiling.”
Since the radiant heating AND a mini duct system together would be too expensive to classify as middle-of-the-road, the mini duct system would work well by itself in my neighbor’s home. We have already established that the existing duct work is leaky and is large enough to accommodate the mini duct system inside it. The air handling unit (AHU) that will be necessary for the mini duct system could be located in the attic or in the basement. In this climate (midwest temperatures) if the AHU is to be located in the attic, an AHU with a heat pump would be a good choice versus an AHU with a hot water coil which might freeze if the system were to fail in the winter.
A hot water coil and a boiler is, however, the more efficient option and would work well if the AHU were located in the basement. With the right equipment selection and application a hot water coil system is more efficient at heating than a heat pump system. The hot water for this system could be generated by either a boiler or a combination domestic water heater and boiler. The combo option would kill two birds with one stone if one was inclined to replace the water heater in the near future anyway. Either choice will likely require a buffer tank to eliminate the chance that the boiler will “short cycle”, or turn on and then off in 5 minutes or less. Short cycling needs to be avoided, as it significantly shortens the life of a boiler.
Another option, if cost is a concern, is to use an electric heating coil in the AHU.
A humidifier is still a good idea with this system, especially because of the “leaky” construction of the house. In the winter, all the drafts that infiltrate through the windows and doors consist of very dry air. To combat that dryness, a whole house humidifier integrated into the AHU should work nicely.
The middle of the road recommendation does not include an insulation retrofit, and therefore an ERV (energy recovery ventilator) will not be necessary either. My neighbor’s “leaky” house, without much of an air or moisture barrier built into the walls [craftsman note: the walls in a couple of the rooms upstairs are pretty cold during the winter months. Makes you want to position the bed in the middle of the room, like a residential island or something], actually results in the desirable effect of ventilating the home. Of course, this is not ideal because it makes the house feel drafty and colder than the thermostat would indicate. Nonetheless, the ventilation needs are met.
Of course, what I want to know is approximately what a retrofit as well as a new installation in a 2000 sq. ft. home would cost. My engineer friend wasn’t willing to venture a guess, so I guess until I’m ready to get an estimate I’ll just have to sit and wonder what the cost of high speed air might be.
My neighborly engineer whipped up something special for me after he read about my 30 year old furnace and how next summer I’m likely going to replace it along with my air conditioning unit that sounds like a small turbo engine tucked alongside our home. It’s the first part of a 2 or 3 part series that’ll cover the ins and outs of retrofitting an older home with a new HVAC system. He’ll be grouping his recommendations into three categories: 1) Money no concern, 2) middle of the road, and 3) penny pincher. I’m sure everyone knows what group they’re in so I don’t need to elaborate any further. Just check out what he has to say.
Considering a Heating Ventilation Air Condition (HVAC) retrofit of your older home? There are a million solutions but here are my recommendations for my neighbor’s 1926 Dutch Colonial.
First, a little background on my neighbor’s house. Built in 1926, it likely started with an “octopus” gravity style coal or fuel oil fired furnace, similar to this natural gas fired furnace below. Ain’t she a beauty?
Notice the giant supply ducts coming from the top and the even larger return air ducts at the bottom. The ducts are so large because these furnaces don’t use fans to circulate the air. The heated air simply rises and the cooler air falls. These systems were simple, they always worked, and they used a lot of fuel. And, there is no way to add cooling to this type of system. When the home owner got tired of the high heating bills the furnace would be retrofitted with a natural gas fired 80% AFUE unit, and perhaps that is what is still heating the home today [craftsman note: I think the AFUE is much lower, maybe around 65 or 70%].
Another key bit of history: most homes of this era have been added onto and then added onto again. My neighbor’s house is no exception. What was once the attached garage became the family room, and years later, a second floor master bed and bath were added above that family room. You can bet that HVAC considerations were not primary in the design process. And as a result these rooms, even though well insulated as compared to the remainder of the house, do not heat or cool very well [craftsman note: That’s right. The whole house heats and cools very unevenly].
If Money Is No Object:
I’d recommend eliminating the furnace all together. Yep, rip it out of the basement and reclaim that space for a recreation room or an additional play room for your bratty kids. What do you heat your house with you ask? Radiant under floor heating installed in all areas of the first floor that have a basement underneath. And for those areas that radiant heat is not feasible, I would choose a high velocity, mini duct, multi-zone system fed by an air handler to be located in the attic [craftsman note: What the hell did he just say?]. This duct systemwould feed all rooms in the house, even those with the radiant heating system; that way the same ducts can be used for cooling. Each zone would be individually controlled with its own thermostat [craftsman note: This mini duct system sounds pretty cool. Just to clarify, it delivers a high velocity stream of air quietly and seamlessly into whatever room you choose through little outlets or holes in the ceiling.]
The duct system would also distribute ventilation air to each room. To provide the ventilation, the air handler would be fitted with an energy recovery ventilator. The energy recovery ventilator would bring in outside ventilation air and exhaust air at the same time [craftsman note: In other words the energy recovery ventilator brings fresh air in and take stale air out]. This would reduce energy costs, because you would not have to pay to heat the cold winter air as much. This is because the warm air being exhausted would be used to pre-heat the incoming cold air.
The duct system can be installed within the wall cavities of interior walls without the need to cut into the wall. Recall how large the ducts in my neighbor’s house are, this provides for the alternative: install the mini ducts inside the home’s existing ductwork. Why not just use the existing ducts? The existing ducts are not sealed air tight and are not sized by today’s standards, which will make climate control difficult.
Some older homes are not built “tight”, so ventilation is not an issue. However, this also means that they tend to be drafty and inefficient to heat and cool. This being the case, and because money is no object, I would recommend pouring a low expansion foam insulation (check out this spray foam data sheet) into the wall cavities that both insulates and seals out drafts. Spray foam is a superior product when compared to regular fiberglass batting. Spray foam has an insulation value that is approximately double that of fiberglass and it functions as an air and moisture barrier as well (read more about spray foam insulation) With the spray foam in place, the home will mimic today’s “tight” construction, which will be much less drafty and more efficient. But, it will now require mechanical ventilation.
With this recommendation there is one more add-on that is worth considering based on the climate my neighbor lives in. Michigan has cold, dry winters, and to combat the low winter humidity a whole house humidifier coupled with the air handler is a good idea. Another thought: I would skip the whole house air filter/purifier. With the energy recovery ventilator in place, I just don’t think it is necessary unless you suffer from allergies, asthma, or other respiratory issues.
That’s all for my “money is no object” recommendation. Although there are more expensive systems available, this one is tailored to your Dutch Colonial.
Well, I don’t know about all that jive engineer talk, but man, I’ve got a HVAC consultant working for me pro bono. How sweet it is. Now I just gotta find me a money tree.
Coming soon – part 2 of the HVAC retrofit series, for those “middle of the road” kind of folks.